1. Field of the Invention
The invention relates to an ink jet recording apparatus for recording by discharging ink and a suction recovery method of the ink jet recording apparatus.
2. Related Background Art
An ink jet recording apparatus is an apparatus for recording by discharging ink from discharge ports of a recording means onto a recording material. The ink jet recording apparatus is used not only for general printing apparatuses but also for apparatuses such as a copying apparatus, a facsimile apparatus having a communication system, a word processor having a printing unit, and the like, and further, for an industrial recording apparatus combined as a hybrid apparatus with various processing apparatuses. In the ink jet recording apparatus for recording by discharging ink droplets from micro discharge ports, a viscosity thickening phenomenon of the ink, an increase in concentration of dye of the ink, fixing of the ink, or the like is caused by evaporation of volatilized ink components from the discharge ports of an ink jet recording head. By leaving for a long period of time, there is a case where bubbles are generated in a liquid chamber of the recording head. When the bubble is generated, the normal supplying operation of the ink is obstructed and, at the worst, the ink is not fed to the head and the recording operation is largely obstructed. To avoid such an inconvenience, there has widely been used a suction recovery method whereby a discharge port surface (face surface) of the recording head is capped, the inside of the cap is depressurized by a pump which has previously been provided in the printer, and the ink is emitted from the discharge port.
Kinds of pumps which are used for the suction recovery are mainly classified into a piston pump and a tube pump. FIG. 21 is an explanatory diagram showing a principle of the piston pump. FIG. 22 is an explanatory diagram showing a principle of the tube pump. FIG. 23 is a graph showing a negative pressure characteristics curve at the time of the suction operation in the tube pump. According to the method by the piston pump, as shown in FIG. 21, a depressurizing chamber 10 communicated with the cap is depressurized by moving a piston. In the piston pump, a suction amount and a suction pressure can be set by changing a movement amount of the piston. According to the method by the tube pump, as shown in FIG. 22, a negative pressure is generated in the cap by using a restoring force of a tube 121 stroked by a roller (pump roller) 120. According to the tube pump, a suction amount and a suction pressure can be arbitrarily set by changing a stroke amount and a stroke speed.
FIG. 23 shows a change in negative pressure with the elapse of time in the case where the inside of the cap is sucked by the tube pump. Referring to FIG. 23, it will be understood that although the suction pressure (negative pressure) increases with the elapse of time in an area A, the generation of the negative pressure by the pump and the elimination of the negative pressure by the emitted ink are balanced and a balance state is obtained in an area B. The negative pressure which provides the balance state is determined in dependence on a flow resistance of the head and ability of the pump upon suction. Ordinarily, the suction recovery operation is executed in the area A. Strictly speaking, suction recovery performance should be specified by the ink flow speed or flow rate. However, the ink flow speed changes with the elapse of time and it is not easy to measure them and quantitatively specify the suction recovery performance. Therefore, the suction recovery performance is generally managed by the suction pressure and the suction amount.
The suction pressure and the suction amount are determined on the basis of the maximum flow rate of the ink from an ink tank for supplying the ink to the recording head, a volume of an ink flow path from an ink supply port of the recording head to the discharge port of the recording head, and the like. When the suction amount is small, the recording head is not sufficiently filled with the ink and an inconvenience occurs. When the suction amount is large, the ink is wastefully consumed. If the bubbles are inserted into the ink flow path of the recording head because, for example, the ink tank is not attached, the empty consumed ink tank has been attached, or the like, it is necessary to remove the bubble by the suction recovery operation. At this time, when the suction pressure is too low, the bubble cannot be sucked, and when the suction pressure is too high, the ink flow speed from the discharge port of the recording head increases, the ink flow rate exceeds the maximum ink flow rate from the ink tank, and the bubbles instead of the ink are fetched from the ink supply port, so that an inconvenience occurs.
In the suction recovery using the tube pump, as disclosed in, for example, Japanese Patent Application Laid-Open No. 2001-063102, the following suction recovery operation is executed: the tube pump is continuously rotated, the inside of the cap is rapidly set to a target negative pressure, and after that, the driving/stop of the tube pump are repeated a plurality of number of times, thereby maintaining the inside of the cap toga value within a predetermined range near the target negative pressure so that the negative pressure curve in which the negative pressure is maintained after the pressure in the cap was made to reach the target negative pressure as shown in FIG. 23 is obtained.
However, in association with the improvement of picture quality and throughput of the ink jet recording apparatus, the number of discharge ports of the recording head increases remarkably, so that it becomes difficult more and more to set the suction pressure and the suction amount and it is difficult to execute the suction recovery operation for keeping all of the discharge ports in a good state. That is, with respect to the removal of the bubbles in the ink flow path, a probability that the discharge ports from which the bubbles cannot be perfectly removed still remain is increasing. According to the conventional suction recovery method, since it is necessary to increase a capacity of the pump in order to cope with the above technical problems, it is necessary to enlarge a size of apparatus by a method whereby the number of tubes of the tube pump is increased, or the like.